168 



Annals of the Soutli African Museum. 



The premaxilla forms the whole of the lower and inner borders of the 

 nostrils and covers the front of the snout, passing up as a wedge- 

 shaped bone to lie in front of the nasals, appearing thus to separate 

 them from each other for part of their length. 



The maxilla is a square bone supporting the jugal below the orbit 

 and carrying the tusk which passes downwards and appears below the 

 front part of the orbit. No definite septomaxilla can be seen on the 

 face, although it is probable that one is present. 



'--PO.F 



FIG. 43. Prolystrosaurus natalensis, Htn. Type. No. 3715. x f . 



The nasals form a straight suture behind with the frontals. 

 Anteriorly they lie behind the premaxilla. They also form the insig- 

 nificant nasal bosses. Their width is greatest in front, as posteriorly 

 thev are narrowed bv the encroachment on the top of the snout of the 



V 



prefrontal. 



The prefrontal is large, the lachrymal smaller. The frontals are 

 broad and do not pass behind the postorbital bar. The relations of 

 the bones round the pineal foramen is shown in the figure. 



The outer bar of the temporal vacuity passes backwards and inwards 

 so that the greatest width across the skull is measured at the post- 



